The polyphenylene ether resins have developed significant use as a family of engineering thermoplastic materials that can be extruded or molded into various plastic articles and component parts. These resins are more typically combined with other polymers and/or various additives to upgrade or achieve a particular desirable combination of properties. Methods of their preparation are described in the patent literature, including U.S. Pat. Nos. 3,306,874; 3,306,875; and 3,914,266(Hay) and U.S. Pat. No. 4,092,294(Bennett,Jr., et al.).
In general, the polyphenylene ether resins are prepared by processes involving the oxidative coupling of one or more phenolic compounds in the presence of a metal-amine complex catalyst, typically a copper-amine. The molecular weight of the polymer is in the usual case controlled by the reaction time, with longer reaction times resulting in a polymer having a greater number of units and longer chain length. It has been a practice to use as a controlling standard the intrinsic viscosity of the final polymer, it being generally desirable to obtain viscosities in the range between 0.4 and 0.6 deciliters per gram as measured in chloroform at 25.degree. C.
Blends of polyphenylene ether resin with polystyrene produce molded articles with excellent tensile, impact and thermal properties. The addition of the polystyrene to polyphenylene ether resins increases the melt flow of the polyphenylene ether which, in turn, improves the processing of these blends into injection molded articles. However, in many cases further improvement in the melt flow is desirable.
It has been speculated that the melt flow of polyphenylene ether-polystyrene blends should be upgraded by using a polyphenylene ether having a broader molecular weight distribution. It is theorized that the fraction of polyphenylene ether having a lower molecular weight will increase the melt flow, while the higher molecular weight fraction will serve to maintain the tensile, impact and heat distortion temperature properties of the blends.